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Not sure why you're being downvoted. I've read estimates that Facebook now shows 10% (!) of all U.S. display ad inventory on the internet.

How does that percentage translate in terms of clicks ? Is that also 10% ?

Of course they are lower than average quality impressions. Proportional representation of clicks isn't necessary with that kind of volume.

Do they profit? Or is Zuckerberg still buying his ramen with VC money?

Being able to target ads well doesn't do you any good if you don't have the ad inventory to make use of that advantage. That's Facebook's problem: their users aren't apt to click on ads while on the site, so they don't convert very well, hence a lot of advertisers don't bother and their inventory sucks.

I've never seen an ad on Facebook that highly targeted me. I think that beyond a few niches (like engagement rings) Facebook's targeting works out to be a wash. That's why despite having 300 million users and billions of page views they are only barely profitable.